1. Field
The present disclosure relates to a CNT-polymer complex capable of self-doping by external stimuli and a process for preparing the same. More particularly, the present disclosure relates to a CNT-polymer complex that includes carbon nanotubes (CNT) coated with a block copolymer of a conjugated polymer and a non-conjugated polymer, is neutral and soluble in organic solvents, and is capable of self-doping by external stimuli, as well as to a process for preparing the same.
2. Description of the Related Art
In order for carbon nanotubes (CNT) to exert excellent physical properties in composite materials, a carbon nanotube dispersion technique is required. In order to use effective properties and benefits of a CNT nanoscale, CNT must be well dispersed.
Methods for accomplishing uniform dispersion of CNTs by increasing the compatibility between CNTs and a solvent or polymer may be classified into mechanical dispersion methods and chemical dispersion methods. Mechanical dispersion methods are based on external force such as ultrasonic waves and may provide an unsatisfactory dispersion degree. Chemical dispersion methods are classified into covalent bonding dispersion methods and non-covalent bonding dispersion methods. Covalent bonding dispersion methods include linking a covalent bond directly to the surface of CNTs and generate surface defects, and thus they may cause degradation of electrical properties. Therefore, covalent bonding dispersion methods are problematic in that they are not suitable for applications using electrical properties. On the contrary, non-covalent bonding methods use a material capable of interaction with the surface of CNTs and generate no defects in the structure of CNTs. Therefore, non-covalent bonding methods are advantageous in that they allow CNTs to exert their unique physical properties. As an example of such non-covalent bonding dispersion methods, a conjugated polymer surrounds the surface of CNTs with ease, thereby increasing the solubility of CNTs.
Meanwhile, conjugated polymers undergo a rapid increase in electrical conductivity by doping. In general, such doping methods include p-doping using an electron acceptor (e.g. I2, AsF5) causing partial oxidation and n-doping using an electron donor (e.g. Na, K) causing partial reduction. Introduction of a dopant generates a partial charge defect and reduces a band gap. As a result, it is possible to accomplish improvement of electrical properties, including an increase in conductivity or hole mobility. A PEDOT/PSS complex including a poly(3,4-ethylenedioxythiophene (PEDOT) as a conductive polymer and a polystyrene sulfonate (PSS) as a dopant is commercially available as aqueous solution due to PSS which is an ionic polymer. The complex is disadvantageous in that it undergoes degradation of long-term shelf stability in the state of aqueous solution due to ionic groups. In addition, the complex exists as an acid or base, and thus may cause damages to a substrate during a solution process, which may affect electronic devices significantly.
When dispersing carbon nanotubes by using such a conjugated polymer doped with an acid or base, dispersion is possible based on non-covalent bonding. However, in this case, pH and water dispersion may be problematic and cause damages to a substrate in applying to organic electronics, which affects electronic devices significantly.